the main question is regular servicing.the owner should know all about the maintance needed for that particular unit & records to show.a unit with 500hr on the clock But not serviced is a poor choice .i am a little over the top when it comes to looking after my units,servicing is done well within the manufactures recomendations.But these are the things that make you a LOT of money,so i look after them,i carry a large stock of spare parts for my units.i have not had a days down time is nearly 2 years.Lee G